This invention relates to a tape protecting cover for a video tape cartridge, especially a tape protecting cover provided with a grooved shaft integrally formed on said tape cover which is adapted to be mounted to a case body. The groove retains a spring for biasing the cover towards the case body. Further, this invention relates to metallic molds for forming a shaft having a groove for retaining the spring of the protecting cover of a video tape cartridge formed by injection molding of a synthetic resin.
A video cartridge containing a video tape therein has a tape protecting cover prepared by injection molding of a synthetic resin, which covers the front portion or opening of a case body consisting of upper and lower pieces. The tape protecting cover is adapted to be opened to allow the tape in the video tape cartridge to be drawn out toward a rotary head side when the video tape cartridge is loaded in a video tape recorder, and to be closed to protect the tape when the video tape cartridge is taken out from the video tape recorder. For this purpose, shafts are provided at both end portions of the tape protecting cover, one of said shafts being inserted in a hole formed in the case body, while the other shaft inserted in another hole in the case body and is provided with a spring for biasing the tape protecting cover in a stationary closed status, whereby said protecting cover is rotatively mounted to the case body. FIG. 1 shows the secured status of the tape protecting cover 2 and the case body 4, in which the tape protecting cover 2 and the case body (upper case body) at the side of the shaft 8 provided with the spring 6 is shown. In general, a coil spring is used as the spring 6, one end 6a of the coil spring abutting against the case body 4 and the other end 6b being secured to the shaft 8. More specifically, the shaft 8 is provided with a groove 10 which receives the end 6b of the spring 6 extending transversely from the axial end to a fixed length as shown in FIG. 2, whereby the spring is permitted to be loaded onto the shaft 8 in the X direction.
The tape protecting cover 2 having the above structure is prepared integrally by injection molding of a synthetic resin. In this case, heretofore, in order to make the shaft having groove 8 to be a cylindrical type provided with such a groove, such process as shown in FIG. 3 is adopted wherein two molds 12 and 14 having semi-cylindrical dents 16 and 18 are prepared and both molds 12 and 14 are allowed to move in a direction shown by the arrow Y to close on each other, thereby forming a cylindrical molding space having a complementary shape for the shaft 8. A resin is poured into the space to form the shaft 8 followed by the steps of separating both molds 12 and 14 after cooling and solidification. The plane 20 of the mated surface of the molds 12 and 14 (parting line) is so formed that the plane 20 passes through the axis of the shaft 8. Further, a rectangular pin 22 which is to form the groove 10 is provided so that the end surface 22 of rectangular pin 22 abut against the wall surface 16a positioned at the most inner portion of the semi-cylindrical dent 16 of the first mold 12 and extends in the Y direction. The depth of the groove 10 of the shaft 8 is preferably as deep as possible and extends across the axis of the shaft 8. Therefore, the front side 22b of rectangular pin 22 protrudes over the parting plane 20 from the mold 12. Accordingly, when both molds are closed on each other, front side 22b of the rectangular pin 22 protrudes into the dent 18 of the second mold 14.
When the shaft having the groove 8 of the tape protecting cover is molded by injection using the molds 12 and 14 described above, the end portion 22a of the rectangular pin 22 provided in the first mold 12 contacts with the end surface 18a at the most inner portion of the second mold 18. At this time, if the end surface 22a of the rectangular pin 22 does not contact closely with end surface 18a of the second mold 18, a clearance occurs between end surface 18a and end surface 22a and the resin is deposited in this clearance to form a burr. The control of the contact between the end surface 22a of such rectangular pin 22 and the end surface 18a of the mold 18 is difficult and prevention of the occurrence of the burr is difficult. Further, such burr also occurs by wearing of the rectangular pin 22 due to use. Accordingly, in the conventional shaft having a groove for securing the spring, the burr is generally formed soon after initial molding operations. Therefore, the extra subsequent work for removing of the burr is necessary after injection molding. This causes complication of the manufacturing process and lowers the efficiency of mass production, thereby increasing the cost of products.